1. Field of the Invention
The present invention relates to a drop/insert processing circuit in a broadband subscriber network.
As a broadband subscriber network, a synchronous optical network (SONET) has been developed in which a broadband subscriber loop system based on a single-mode fiber is employed, and high speed data is run through the loop. Terminal units dealing with low speed data are connected to the broadband subscriber loop, and therefore, drop/insert processing circuits must be connected between the high speed data loop and the low speed data terminal units, for dropping data from the loop or for inserting data into the loop.
The circuit scale of the drop/insert processing circuit, however, is too large and must be reduced, and the control of the drop/insert processing must be simplified.
2. Description of the Related Art
As a prior art of the present invention, a paper entitled "SONET" by Rodney J. Boehm, Yan-Chau Ching, and Rand C. Sherman, Bell Communications Research, Navisink Research Engineering Center, 331 Newman Springs Rd., CH 2190-7/85/0000-1443$1.00 1985 IEEE, describes a multiplexing and demultiplexing technology.
The above prior art and other conventional drop/insert processing circuits have the above-mentioned disadvantage of a large circuit scale, because the dropping circuit and the inserting circuit are separately provided as described in more detail with reference to the drawings, or have the above-mentioned disadvantage of a complex control.